15868( 2) - 24-Jul-2019 14:05:19 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15868 Version: 2 Check-in Time: 24-Jul-2019 14:05:19 STScI Edit Number: 0 Title Constraining the UV-absorbing material on Jupiter's icy moons through comparative reflectance spectroscopy ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Pippa Molyneux Southwest Research Institute Y CoI: Dr. Tracy M Becker Southwest Research Institute N CoI: Dr. Emilie Royer Planetary Science Institute N CoI: Dr. Kurt David Retherford Southwest Research Institute N ------------------------------------------------------------------------------------ Abstract The far-UV (FUV) spectrum of water ice contains a sharp absorption edge around 165 nm, becoming highly reflective at wavelengths longer than this. This feature has been observed in lab measurements and in Cassini UVIS observations of Saturn's moons. However, Ganymede's FUV spectrum (derived from COS G140L observations in 2014) does not exhibit a sharp increase in reflectance near 165 nm as expected; instead, the reflectance gradually increases at wavelengths >170 nm, implying that there is a UV-absorbing contaminant present. Observations of Europa just outside of the critical region around 165 nm suggest that the water ice feature may be similarly modified there, and Callisto's reflectance in this region is currently unknown. We therefore propose to observe Europa and Callisto using COS G140L, to determine whether the spectral reflectance of the two moons close to the 165 nm water ice edge is modified similarly to Ganymede's. We will use four HST orbits to observe the leading and trailing hemispheres of each satellite. The leading and trailing hemispheres of the Galilean moons experience different radiation environments, with Jovian magnetospheric plasma predominantly impacting the trailing hemispheres. By comparing the observed reflectance of Jupiter's icy moons, and by assessing differences between the leading and trailing hemispheres, we can investigate whether a single contaminant modifies the spectra of all three satellites, and whether this may be a product of radiolytic processing of the surfaces by the Jovian plasma. ------------------------------------------------------------------------------------ Observations Description ------------------------ The orbital leading and trailing hemispheres of Europa and Callisto will each be observed in four single orbit visits, using the COS G140L grating with central wavelength setting 1280. We have requested observations within +/- 6 weeks of Jupiter opposition to maximize the angular size of the targets, but if scheduling is a problem we can relax this slightly. We plan to use the same target acquistion strategy as used in program 13328 for FUV observations of Ganymede. That program followed the ACQ/SEARCH with a COS/NUV ACCUM exposure to verify Ganymede's position in the aperture. We have not included this step because we do not require precise centering information, and because programs 13803 and 14903 successfully observed Europa with COS following a single ACQ/SEARCH exposure. 15868( 2) - 24-Jul-2019 14:05:19 - [ 2] For ETC target acquisition runs we used surface brightness values from JPL Horizons (Europa: 5.2 Vmag/arcsec2; Callisto: 6.5 Vmag/arcsec2) and scaled them based on the difference between the visible and NUV albedos of Europa and Callisto. Europa's visible albedo is ~67%, and its average albedo in the 240-320 nm range is ~ 13% (trailing hemisphere) to ~27% (leading hemisphere) [Nelson et al. 1987], so it is ~1 to 1.8 magnitudes dimmer in the NUV. Callisto's visible albedo is ~22%, its average albedo in the 240-320 nm range is ~5.2% (leading hemisphere) to ~ 7.5% (trailing hemisphere), and it is therefore ~1.2 to 1.6 magnitudes dimmer in the NUV. ETC runs for the science exposures used Ganymede COS G140L data from Program 13328 as input spectra. Europa may be up to ~1.6 x brighter than Ganymede at wavelengths >160 nm, based on the ratio of their NUV albedos, but even if this is the case the maximum count rate will be well below the COS FUV count rate limits. ------------------------------------------------------------------------------------ 15868( 2) - 24-Jul-2019 14:05:19 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: EUROPA-EAST ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE SATELLITE EUROPA ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=JUPITER STD=EUROPA ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS NOT OCC OF EUROPA-EAST BY JUPITER FROM EARTH, SEP OF EUROPA-EAST IO FROM EARTH GT 10", SEP OF EUROPA-EAST GANYMEDE FROM EARTH GT 10", SEP OF EUROPA-EAST CALLISTO FROM EARTH GT 10", OLG OF EUROPA-EAST BETWEEN 75 105 ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 5.3 +/- 0.5 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 TARGET NAME: EUROPA-WEST ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE SATELLITE EUROPA ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=JUPITER STD=EUROPA ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS NOT OCC OF EUROPA-WEST BY JUPITER FROM EARTH, SEP OF EUROPA-WEST IO FROM EARTH GT 10", SEP OF EUROPA-WEST GANYMEDE FROM EARTH GT 10", SEP OF EUROPA-WEST CALLISTO FROM EARTH GT 10", OLG OF EUROPA-WEST BETWEEN 255 285 ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 5.3 +/- 0.5 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 15868( 2) - 24-Jul-2019 14:05:19 - [ 4] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 TARGET NAME: CALLISTO-EAST ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE SATELLITE CALLISTO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=JUPITER STD=CALLISTO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS NOT OCC OF CALLISTO-EAST BY JUPITER FROM EARTH, SEP OF CALLISTO-EAST IO FROM EARTH GT 10", SEP OF CALLISTO-EAST EUROPA FROM EARTH GT 10", SEP OF CALLISTO-EAST GANYMEDE FROM EARTH GT 10", OLG OF CALLISTO-EAST BETWEEN 75 105 ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 5.6 +/- 0.5 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 4 TARGET NAME: CALLISTO-WEST ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE SATELLITE CALLISTO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=JUPITER STD=CALLISTO ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS NOT OCC OF CALLISTO-WEST BY JUPITER FROM EARTH, SEP OF CALLISTO-WEST IO FROM EARTH GT 10", SEP OF CALLISTO-WEST EUROPA FROM EARTH GT 10", SEP OF CALLISTO-WEST GANYMEDE FROM EARTH GT 10", OLG OF CALLISTO-WEST BETWEEN 255 285 ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 5.6 +/- 0.5 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 15868( 2) - 24-Jul-2019 14:05:19 - [ 5] Visit: 01 (ELead) Visit Requirements: BETWEEN 02-JUN-2020:00:00:00 AND 25-AUG-2020:00:00:00 On Hold Comments: Additional Comments: Europa leading hemisphere Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 EUROPA-EAST COS/NUV ACQ/SEA BOA MIRRORA SCAN-SIZE=2 1 3 S (3 S) RCH Comments: ETC run assumes surface brightness of 6.1 Vmag/arcsec2 ------------------------------------------------------------------------------------------------------------------------------------ 2 EUROPA-EAST COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=930, FP-POS=1 1 950 S G see below (1035 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 EUROPA-EAST COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=930, FP-POS=2 1 950 S G see below (1035 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ EUROPA-EAST 1 COS/NUV ACQ/SEA BOA MIRRORA none none none none 1 N/A RCH EUROPA-EAST 2 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 1035.0 S G EUROPA-EAST 3 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 1035.0 S G 15868( 2) - 24-Jul-2019 14:05:19 - [ 6] Visit: 02 (ETrail) Visit Requirements: BETWEEN 02-JUN-2020:00:00:00 AND 25-AUG-2020:00:00:00 On Hold Comments: Additional Comments: Europa trailing hemisphere Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 EUROPA-WEST COS/NUV ACQ/SEA BOA MIRRORA SCAN-SIZE=2 1 3 S (3 S) RCH Comments: ETC run assumes surface brightness of 7.0 Vmag/arcsec2 ------------------------------------------------------------------------------------------------------------------------------------ 2 EUROPA-WEST COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=930, FP-POS=3 1 950 S G see below (1035 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 EUROPA-WEST COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=930, FP-POS=4 1 950 S G see below (1035 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ EUROPA-WEST 1 COS/NUV ACQ/SEA BOA MIRRORA none none none none 1 N/A RCH EUROPA-WEST 2 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 1035.0 S G EUROPA-WEST 3 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 1035.0 S G 15868( 2) - 24-Jul-2019 14:05:19 - [ 7] Visit: 03 (CLead) Visit Requirements: BETWEEN 02-JUN-2020:00:00:00 AND 25-AUG-2020:00:00:00 On Hold Comments: Additional Comments: Callisto leading hemisphere Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CALLISTO-EA COS/NUV ACQ/SEA BOA MIRRORA SCAN-SIZE=2 1 5 S (5 S) ST RCH Comments: ETC run assumes surface brightness of 8.2 Vmag/arcsec2 ------------------------------------------------------------------------------------------------------------------------------------ 2 CALLISTO-EA COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=930, FP-POS=1 1 950 S ST G see below (1031 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 CALLISTO-EA COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=930, FP-POS=2 1 950 S ST G see below (1031 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ CALLISTO-EAST 1 COS/NUV ACQ/SEA BOA MIRRORA none none none none 1 N/A RCH CALLISTO-EAST 2 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 1031.0 S G CALLISTO-EAST 3 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 1031.0 S G 15868( 2) - 24-Jul-2019 14:05:19 - [ 8] Visit: 04 (CTrail) Visit Requirements: BETWEEN 02-JUN-2020:00:00:00 AND 25-AUG-2020:00:00:00 On Hold Comments: Additional Comments: Callisto trailing hemisphere Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CALLISTO-WE COS/NUV ACQ/SEA BOA MIRRORA SCAN-SIZE=2 1 5 S (5 S) ST RCH Comments: ETC run assumes surface brightness of 7.6 Vmag/arcsec2 ------------------------------------------------------------------------------------------------------------------------------------ 2 CALLISTO-WE COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=930, FP-POS=3 1 950 S ST G see below (1031 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 CALLISTO-WE COS/FUV TIME-TA PSA G140L 1280 BUFFER-TIME=930, FP-POS=4 1 950 S ST G see below (1031 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ CALLISTO-WEST 1 COS/NUV ACQ/SEA BOA MIRRORA none none none none 1 N/A RCH CALLISTO-WEST 2 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 1031.0 S G CALLISTO-WEST 3 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 1031.0 S G 15868( 2) - 24-Jul-2019 14:05:19 - [ 9] Summary Form for Proposal 15868 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures BOA, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/SEARCH, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=930, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4, SCAN-SIZE=2 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 02-JUN-2020:00:00:00 AND 25-AUG-2020:00:00:00 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names CALLISTO-EAST, CALLISTO-WEST, EUROPA-EAST, EUROPA-WEST ------------------------------------------------------------------------------------------------------------------------------------